Frequency of vavilovoid mutants induced by radiation and chemical mutagen treatments in durum wheat

R. M. DESAI and C. R. BHATIA

Biology and Agriculture Division, Bhabha Atomic Research Centre, Bombay 400 085, India

Occurrence of vavilovoid mutants in mutagenised populations of tetraploid and hexaploid wheat have been reported. These mutants phenotypically resemble Triticum aestivum ssp. vavilovi (TUM) SEARS first described by JAKUBZINER. The vavilovoid mutants are slow growing with slender weak culms and narrow leaves. Their spikes show pseudobranching which is due to increased length and number of rachillae nodes, non-free-threshing habit, basal sterility and reduced development of awns in the speltoid background. The seed set is usually very poor.

In our mutation experiments with durum wheat cultivar Vijay, a number of M₂ families were found to segregate for the vavilovoid mutants (Fig. 1). A significant finding, however, was that all these segregating families were derived from seeds treated with chemical mutagens - ethylmethane sulfonate (EMS), N-methyl-N-nitrosourea (MNU) and N-ethyl-N-nitrosourea (ENU) (Table 1). None of the families originating from gammaray or neutron irradiated seeds segregated for vavilovoid mutants. As is evident from Table 1, a large number of families and plant populations have been scored both in radiation and chemical mutagen treatments. Though vavilovoid mutants have been obtained in durum wheat and in T. carthlicum following X-irradiation of seeds, the observed differences in the frequency of vavilovoid mutants in the radiation and chemical mutagen treatments in the present study could not be due to the chance alone. Further, data of PRASAD show that both in durum and carthlicum such mutants occurred in chemical treatments or in combination treatments of gamma-rays and chemicals. Vavilovoid mutants did not occur in gamma-ray treatments.

The vavilovoid phenotype is believed to result from mutation at a locus situated on the long arm of chromosome 5A between the q gene and the awn inhibitor B₁ and its expression is suppressed by the free-threshing gene Q. It is, therefore, inferred that in a free threshing durum cultivar only simultaneous mutation for both speltoidy and vavilovoidy can lead to vavilovoid phenotype.

Chemical mutagens are more effective than radiations in inducing chlorophyll mutations in hexaploid wheat and such mutants are presumed to result from intragenic changes. Further, numerous morphological mutations not observed following radiation treatments were induced by chemical mutagens like EMS. From the present study also it is evident that the vavilovoid mutants are readily induced by chemicals as compared to radiations in durum wheat. It implies that chemical mutagens may be more efficient than radiations in inducing the type of intragenic changes which will result in vavilovoid mutations.

(Received July 19, 1974)